As is known, systems for harvesting energy (also known as “energy-harvesting systems” or “energy-scavenging systems”) from environmental-energy sources have aroused and continue to arouse considerable interest in a wide range of fields of technology. Typically, energy-harvesting systems are designed to harvest (or scavenge) and store energy generated by mechanical sources, and to transfer it to a generic load of an electrical type. In this way, the electrical load does not require batteries or other power-supply systems, which are frequently cumbersome, have a low resistance to mechanical stresses, and entail costs of maintenance for interventions of replacement.
The environmental energy may be harvested from different available sources and converted into electrical energy by purposely provided transducers. For example, available energy sources may be mechanical or acoustic vibrations or, more in general, forces or pressures, chemical energy, electromagnetic fields, environmental light, thermal energy. For harvesting and conversion there may be used, for example, electrochemical, electromechanical, piezoelectric, electroacoustic, electromagnetic, photoelectric, electrostatic, thermoelectric, thermoacoustic, thermomagnetic, thermoionic transducers, etc.
Between the transducers and the storage element a harvesting interface (or “harvesting front-end”) is normally used, which has the task of receiving the electrical signals supplied by the transducers and supplying a recharging current to the storage element. Harvesting interfaces are designed to present a very high efficiency. In order to function, in fact, the harvesting interfaces must absorb from the storage element an amount of energy, which obviously is no longer available for supplying the load.
A problem constantly present in energy harvesting depends upon the fact that the available sources are usually discontinuous and hence the flow of energy to the storage element may be interrupted. For example, in the case where the energy source is represented by mechanical vibrations or environmental light, a condition of rest or of darkening, respectively, may temporarily substantially annul harvesting and storage of energy from the environment. The harvesting interface continues, however, to receive power-supply energy from the storage element, which tends to run down. However well designed the harvesting interface may be, the consumption in the absence of environmental energy available reduces the overall efficiency of the energy-harvesting system.
It would hence be desirable to reduce the consumption of the harvesting interface when the transducer is not in a condition to receive energy from the environment. In addition, the energy-harvesting system must be able to respond to the activity of the transducer to prevent part of the energy received by the transducer itself from being dispersed.